1. Field of the Invention
The present invention relates to a microphone adaptor for a respirator and particularly, but not exclusively, to such an adaptor for use with a nuclear, biological and chemical (NBC) respirator of the type worn by service personnel
2. Prior Art
Defence organisations throughout the World have for many years supplied soldiers and other service personnel with respirators to protect them from NBC exposure. Respirators are normally in the form of a full face mask protecting the complete face of the service personnel wearing them including the eyes. The respirator seals tightly against the face to ensure that air breathed is drawn in through an appropriate filter and exhaled through a one way non-return valve (exhale valve).
Respirators are normal made out of a rubber type material so that they are flexible enough to permit a standard issue respirator to fit and seal against the many varied face shapes that may find themselves wearing such a respirator. Unfortunately, the materials respirators are normally manufactured from are not particularly efficient at transmitting acoustic sound waves and thus there is a problem permitting service personnel to communicate, with each other either directly or via radio, when they are wearing NBC respirators.
Originally, the problem with radio communications was addressed by having a microphone mounted to the front of a respirator through which an operative could communicate with a radio. However, this did not solve the problem of enabling the operative to communicate with his immediate colleagues by direct speech. To solve this problem some respirators now incorporate a speech projector mounted in front of the respirator in front of the operatives mouth. One such respirator is the S10 used by the British Army, seen in FIGS. 1 and 2 on the accompanying drawings (FIG. 2 being a cross section along the line 1-1 of FIG. 1). The speech projector enables the operative to talk, or shout, directly to his colleagues, but this has necessitated relocation of the microphone for his radio and a speech diaphragm has been incorporated at the side of the mask to which a standard issue microphone may be fitted, either by clipping or screwing over the speech diaphragm. The speech diaphragm is adapted to be “sound transparent” relative to the other material of the respirator whilst ensuring a complete seal to ensure protection of the operative whether or not the microphone is fitted, or fitted incorrectly.
Respirators typically comprise an inner face seal, which is between the mouth of the operative and the speech diaphragm. This inner face seal degrades speech reaching the speech diaphragm and indeed the speech diaphragm itself is not perfectly transparent to speech. Thus, speech received by a microphone mounted to the speech diaphragm is of relatively poor quality compared to speech that would be received directly from the operative.
In addition to the above problem, of transmission of speech through the inner seal and the speech diaphragm, the performance of a respirator microphone in high background noise is also poor because the coupling to the microphone has to be open to the air otherwise a pressure wave between the microphone and the respirator further distorts speech.